Weird bug with pruneLength and Chinese text

[lucasholder]

Description

When the Chinese text in a MDX file is too long, excerpt(pruneLength: 250) returns an empty string. When the text is a bit shorter, it returns the expected string of length 250.

Steps to reproduce

I'm a gatsby noob, not sure how to make a smaller reproduction of the bug... Basically, I did gatsby new gatsby-prunelength-bug https://github.com/vim-labs/gatsby-theme-sky-lite-starter and changed last 2 blog posts, one with long Chinese text and other with shorter Chinese text. Here's the guilty line: https://github.com/vim-labs/gatsby-theme-sky-lite/blob/master/src/templates/home.js#L139

git clone https://github.com/lucasholder/gatsby-prunelength-bug.git;
cd gatsby-prunelength-bug;
npm install;
gatsby develop;

Environment

gatsby 2.19.48

[jlkiri]

Apparently this is a bug in the prune function that gatsby-plugin-mdx uses. Here is the full code:

module.exports = function prune(str, length, pruneStr) {
  str = makeString(str);
  length = ~~length;
  pruneStr = pruneStr != null ? String(pruneStr) : '...';

  if (str.length <= length) return str;

  var tmpl = function(c) {
      return c.toUpperCase() !== c.toLowerCase() ? 'A' : ' ';
    },
    template = str.slice(0, length + 1).replace(/.(?=\W*\w*$)/g, tmpl); // 'Hello, world' -> 'HellAA AAAAA'

  if (template.slice(template.length - 2).match(/\w\w/))
    template = template.replace(/\s*\S+$/, '');
  else
    template = rtrim(template.slice(0, template.length - 1));

  return (template + pruneStr).length > str.length ? str : str.slice(0, template.length) + pruneStr;
};

The particular line c.toUpperCase() !== c.toLowerCase() is the culprit. It returns false for every character in the Chinese string, so the whole result is just whitespace. I think we need to switch it to some new dependency.

[lucasholder]

@jlkiri thanks.. hopefully your fix will get merged soon!

[danabrit]

@lucasholder Can you confirm whether this PR fixed your issue?

[pvdz]

Going to close this due to lack of response. If this is still the case please reopen or open a new issue pointing to this issue. Thanks!